1. Field of the Invention
The present invention relates to a group key update method and system which updates a key of members in a group. More particularly, the present invention relates to a group key update method and a group key update apparatus which can effectively update a key of group members when at least two group members simultaneously leave the group via a batch processing.
2. Description of Related Art
Contents which are provided to group members are typically encrypted, so that other users can not use the contents. Accordingly, all of the group members should have an encryption key, provided from a server, capable of decoding the encrypted contents.
Accordingly, updating an encryption key is an important issue. For example, when a new member joins a group, the group is required to allow the new member to restrictively access contents. Later, after the new member joins the group, when the existing group members update the encryption key, the new member may share the updated key.
Also, when one of the existing group members leaves the group, the group key, used by all group members before the leaving member leaves the group, is required to be updated so that the leaving member no longer has access to the contents.
Generally, methods of updating the group key are performed in two ways.
In one method, a server calculates an updated key and transmits the updated key to a member requiring the updated key, when it is required to update a group key. This method is problematic due to the great burden placed upon the server since the server is required to calculate the group key for all group members who require the updated group key, and then transmit the calculated group key.
In another method, members that are capable and require the update voluntarily calculate the group key and perform a required update, while the server transmits the updated key to only those members incapable of performing a self-update when it is required to update the group key. In the case of this method, the burden placed upon the server is not great since the server calculates to transmit the updated group key to only those members incapable of performing the self-update. However, it is quite difficult for the members that require the update to effectively self-update the group key.
Further, group key updating is more complex when at least two members simultaneously join the group, and the problem of repeatedly updating an updated key may occur.
Accordingly, there is a need for an improved method and apparatus thereof for effectively updating the group key to be capable of performing a self-update.